Chitosan nanocarriers enhance stability and field performance of fTDP against plant viruses.

Although biopesticides possess advantages such as target specificity and environmental friendliness, their inconsistent efficacy under field conditions significantly hinders large-scale adoption and application. fTDP, a protein obtained by prokaryotic fusion expression system, is capable of inducing systemic acquired resistance (SAR) in plants, thereby inhibiting tobacco mosaic virus (TMV) infection and demonstrating significant potential for development as an antiviral biopesticide. In this study, chitosan nanoparticles, loaded with fTDP (CSNPs-fTDP) were prepared by ionic gelation to address the instability of fTDP proteins in field applications. After optimizing the preparation process, the particle size of CSNPs-fTDP was measured to be 273.7 ± 13 nm, with an absolute zeta potential value exceeding 50 mV and a PDI of 0.215 ± 0.003. In pot trials, CSNPs-fTDP and fTDP both induced hypersensitive responses (HR), activated the salicylic acid signaling pathway induced SAR, and enhanced tobacco's defensive enzyme activity and defense-gene expression. In field trials, CSNPs-fTDP treated tobacco had an average TMV control efficacy of 50.7 %, higher than the 39.2 % of fTDP treated tobaccos. In summary, using fTDP and Chitosan, environmental-friendly natural products, we developped CSNPs-fTDP, which has high field stability and good control efficacy. It retains fTDP's disease resistance and growth promotion functions while leveraging the nanoformulation's sustained-release and stabilizing effects, laying the foundation for the nanoformulation of more biosourced materials.